Principle：The development of USR is based on the principle of UASB, sewage with high Content of organic solids(more than 5 percent) was Evenly distributed in the bottom of the reactor by the water distributive system in the bottom, then sewage rise through solid bed with high concentration of anaerobic microorganisms，Because the organic solids in the sewage and anaerobic microorganisms contact fully and respond, organic solids are liquefied, fermented and degraded into biogas. Mixed by the up-rising biogas and the flowing water, organic solids and microorganisms contact fully. For microorganisms and organic solids settle long in the reactor, the organic solids are degraded quickly. Boards are settled before overfall channel in order to reduce the outflow of SS. The biogas enters into the chamber in the top of the reactor through scummy layer and break up the scummy layer. Unnecessary sludge and inert materials are timely ruled out through pipes in the bottom.

Advantages：USR is used for sewage with high content of solids, often more than 5 percent. Sludge Retention Time is long and organic matters are degraded quickly. Sewage was distributed evenly through pipes in the bottom and has the agitation function. USR has no sluge-returned system and gas-liquid-solid three-phase separator. It has high efficiency, simple operation and management, low cost and strong processing volume. It is one of the most widely used anaerobic biological reactors in the world at present.

Fields of Application：It is used for the treatment of waste waters of starch, liquor, sugar, butcher, breed aquatics, paper and leather industries, sludge clear solution and so on sewage with high content of solids.